zelig

A chameleon-like person who can change his or her persona to fit in any
surrounding; one who appears to be present everywhere and unexpectedly
associated with famous people or events.

[After Leonard Zelig, hero of the 1983 movie
Zelig by Woody Allen. In the
movie, Zelig can blend in with people around him: if he is with doctors
he can transform into a doctor; he can take characteristics of anyone:
Hassidic rabbis, obese, Scottish, and so on. The name Zelig is from German
selig (blessed, happy).]